The technical field of this invention is high frequency ultrasonic, or hypersonic, therapy and, in particular, the use of such therapies for thermokeratoplasty (heat-induced modifications of the shape of the cornea) and other surgical procedures based on controlled hyperthermia.
In recent years, researchers have developed a wide range of therapeutic and surgical procedures utilizing the application of localized hyperthermia at selected target sites within human patients. These techniques include destruction of tumors, ophthalmological procedures, such as eye thermokeratoplasty, and sealing of small blood vessels to reduce bleeding during surgery. Various types of apparatus have been employed to deliver this localized heat, including torches, heated needles, electric scalpel, microwave devices, lasers, and ultrasound generators.
The predictability, controllability and safety of thermokeratoplasty and other hyperthermia procedures is largely dependent upon accurate control of the location and temperature of the hyperthermia zone in the human tissue, as well as the duration of the heating. In particular, the success of many hyperthermia-based surgical and therapeutic procedures requires precise control of the space/time profile of the hyperthermia applied to the target tissue. An additional requirement is the avoidance of excessive overheating of, and damage to, surrounding tissue.
Appreciation of these requirements has led many researchers to the conclusion that virtually all conventional hyperthermia techniques have serious shortcomings. In particular, it is impracticable to utilize a thermal source to selectively deliver heat to target volumes of tissue through thermal diffusion, because when the distal portions of the volume are heated to the desired temperature, severe overheating of the tissue in direct contact with the source occurs.
Laser thermokeratoplasty methods offer alternatives to conventional, physical contact hyperthermia. Such techniques involve the application of a beam of infrared radiation into the tissue volume. However, the application of infrared lasers to generate localized heating often relies upon the balancing of intensity enhancement in a focused laser beam and the optical attenuation presented by tissue material, factors that sometimes are not precisely controllable. In addition, the laser approach is expensive and requires a large supporting apparatus.
It is, accordingly, an object of the invention to provide improved methods and apparatus for generating hyperthermia.
It is another object of the invention to provide hyperthermia methods and apparatus utilizing a source of radiation that deposits energy into tissue in a controllable manner.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.